The piston valve in a musical instrument such as a trumpet is pushed down to change the note played. A typical trumpet has three valve casings each with a piston valve assembly. Each valve casing is connected to a valve slide. If the piston valve is in the up position, the air through the trumpet will take the shortest possible path through one port in the piston valve. When the piston valve is pushed down, the air is diverted through a different port in the piston valve, around the valve slide, and back out through another port in the piston valve.
A typical top spring piston valve assembly inserted into a valve casing includes a finger button on top of a valve stem the distal end of which is fastened to a valve barrel also called a spring barrel, sleeve, baluster, or spring case section. A separate piston with air ports is soldered to the valve barrel. A spring in the valve barrel in combination with a valve guide or “star” biases the entire piston valve assembly (and the finger button) in the up position.
Specifically, the valve guide, washer-like in construction, is adapted for sliding engagement with longitudinal opposing guide slots in the valve barrel as the spring in the valve barrel is compressed. Thus, when the finger button is pushed down, the stem, the valve barrel, and the piston move down as a unit. The valve guide remains stationary since it is fixed vertically with respect to a ridge (also called a seat, ledge, shelf, or shoulder) in the valve casing. The button, stem, valve barrel, and piston are biased upward due to the compression of the spring between the valve guide and the valve stem. The valve guide, by cooperating with grooves and the ridge in the valve casing, also orients the entire piston valve assembly both radially and longitudinally in the valve casing most notably to correctly orient the ports in the piston portion of the valve with the trumpet slides.
Those skilled in the art have attempted to provide tension adjustment for the spring in the valve barrel. See U.S. Pat. Nos. 2,149,714 and 1,367,386. U.S. Pat. No. 3,990,342 discusses up stroke and down stroke adjustment of a piston valve. U.S. Pat. No. 2,511,255 shows a self lubricating piston valve. All of these patents are incorporated herein by this reference.
The alignment of the valve piston ports to the slides, however, has always been problematic. Valves are not made to consistently high tolerances and often slides are not positioned to consistently high tolerances either. Valve radial position inaccuracy can also easily occur during the soldering operation when the valve barrel is soldered to the valve piston. If the tooling used is worn, or if the heat of the soldering operation causes part movement, the result can be an inaccurately placed valve. Indeed, many brass instrument owners send their instruments, both old and new, to specialists for a “valve alignment job”. These specialists attempt to determine by how much each valve is misaligned. To correct radial misalignment they then unsolder the valve barrel from the piston and solder the two parts back together in a position where the craftsman believes the alignment will be correct. Since there is no practical way to easily measure the precise amount of radial misalignment, the repositioning of the valve barrel to the piston is not always correct and the valve alignment process may need to be repeated. Vertical realignment is accomplished by changing rubber and felt washers.
Valves are also costly to make. In order to manufacture the valve, one machining operation has to be performed to make the valve barrel, and a separate machining operation has to be performed to make the piston. As indicated above, the two parts then have to be soldered together in what is typically a manual operation.